Genesis of Chromitites From the Mantle and Crust–Mantle Transition Zone: Constraints From the Bursa Ophiolite, NW Turkey

ABSTRACT

Ophiolitic chromitites are critical archives of mantle melt transport and ore formation in supra‐subduction zone (SSZ) settings, occurring as two distinct ore styles: mantle‐hosted podiform and crust–mantle transition zone (CMTZ)‐hosted stratiform‐like orebodies. However, their genetic linkage remains poorly constrained. The Bursa ophiolite, northwestern Turkey, exposes complementary levels of a single oceanic lithospheric mantle section across the Harmancik and Orhaneli massifs, enabling forearc melt evolution to be traced from deep mantle reaction channels to shallow CMTZ melt‐focusing systems. Harmancik comprises fertile lherzolites recording 6%–13% partial melting and refractory harzburgites recording 15%–20% melting, both overprinted by migrating forearc melts and associated with replacive dunite channels and podiform chromitites. In contrast, Orhaneli exposes CMTZ dunite–chromitite assemblages and ultramafic–mafic cumulates, recording shallow melt focusing, magmatic differentiation, and in situ crystal accumulation. These observations suggest that the Bursa chromitites represent a vertically linked ore‐forming system in which mantle‐hosted podiform chromitites formed in reaction channels, whereas CMTZ‐hosted stratiform‐like chromitites formed during upward melt focusing, differentiation, fractional crystallisation, cumulus processes, and multistage melt percolation.